Can taking aspirin or ibuprofen reduce your risk of getting breast cancer? One of the largest studies of its kind suggests that the answer might be yes.

Taking aspirin and ibuprofen may lower risk of breast cancer, but more research is needed, experts say.

In the past, researchers have flip-flopped on the issue, so they recently combined some of the best data - from 2.7 million women in 38 separate studies - to look for solid evidence. And they found it.

Women who took aspirin had a 13 percent lower risk of breast cancer than those who didn't, while those who took ibuprofen had a 21 percent lower risk.

While it might be tempting to try to reduce your own risk by popping these over-the-counter pain relievers, known as nonsteroidal anti-inflammatory drugs (NSAIDs), the researchers sound a note of caution: The pills can cause bleeding in your digestive tract. And some types of NSAIDs have been linked to risk of heart problems. Health.com: How aspirin can help your heart

"I would not recommend that women use NSAIDs for breast cancer prevention," says study author Bahi Takkouche, M.D., Ph.D., of the University of Santiago de Compostela in Spain. "NSAIDs may have very strong secondary effects. The results of this study just show that women who are taking NSAIDs for other reasons probably have a lower risk of breast cancer." Health.com: How to cut your breast cancer risk at any age

This type of study can't prove conclusively that NSAIDs are responsible for the lower risk of breast cancer. According to the experts, some other factor could be responsible for the reduction in cancer risk.

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However, the link is plausible, says coauthor Mahyar Etminan, Pharm.D., of the University of British Columbia in Vancouver.

"[NSAIDs] are strong inhibitors of the enzyme cyclooxygenase -- COX -- which is an important enzyme that is responsible for producing inflammatory mediators," Etminan says. "Inflammation and inflammatory mediators are thought to be important in the pathology of [breast cancer]."

Research in animals suggests that NSAIDs might be more helpful fighting certain types of breast cancer than others -- which could explain why past studies in women with breast cancer have had mixed results. For example, there's some evidence that NSAIDs may be more effective at preventing cancers that over-express the HER2 gene, according to an editorial published with the study.

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MayoClinic.com: Breast cancer

Etminan says the first randomized controlled trial looking at NSAIDs and cancer is now under way in the United Kingdom. In the study, known as the REACT trial, women at high risk for breast cancer are taking celecoxib to see whether the drug can lower their risk. If this and other large trials show that NSAIDs are truly effective, then doctors may start to recommend them to women for breast cancer risk reduction. Health.com: My breast cancer diary in pictures

"As of today, NSAIDs should not be part of any breast cancer therapy," Etminan says.